Tire having reinforcement ply with discontinuous substantially circumferential metal wires or cables

ABSTRACT

A tire, having at least one carcass reinforcement, furthermore comprises  itional reinforcement ply (1) of maximum circumferential length L, composed at least of lengths (20) of metal wires or cables, of lengths of between 0.1 L and 0.5 L, arranged substantially circumferentially, parallel to each other and forming rows separated from each other, in the direction perpendicular to their orientation, by gaps (p, P), characterized in that a textile cord or cable (3) of synthetic material is present in at least one gap out of two, and continuous over the entire length of the rows.

BACKGROUND OF THE INVENTION

The present invention relates to a tire with radial carcassreinforcement furthermore comprising a reinforcement formed of at leastone ply of reinforcement elements which is composed of wires or cablesforming an angle of between 0° and 15° with the circumferentialdirection of said tire. It also relates to the method of production ofsaid ply from a strip of wires and/or cables.

In the case of a tire for a passenger vehicle, the ply or plies ofcircumferential elements are generally crown reinforcement plies ofcontinuous polyamide cables, and in particular aliphatic polyamide,these cables permitting a certain elasticity while permitting, owing totheir property of contractility under the action of heat, major hoopingof the subjacent plies, which are generally of metal and formed ofcables forming a certain angle, generally between 10° and 45°, with thecircumferential direction.

This type of textile cable is not recommended for use in largequantities in crown reinforcements for "heavy-goods vehicle" tires, inparticular for so-called highway tires. In fact, the afore-mentionedmaterial gives rise to heating, which is incompatible with a long lifeof the crown of the tire. The use of metal cables is preferable, becausefirstly it results in a lower production of heat in the zones subject toheating, and secondly results in better dissipation of the heatproduced.

The use of substantially circumferential metal cables in a crownreinforcement ply for a "heavy-goods vehicle" tire is not without itsproblems, in particular in the molding of the tire in the vulcanizationmold. Good distribution of the rubber mix of the tread when the curingpress is closed and vulcanization begins requires the tire, in thenon-vulcanized state, to have a tread diameter, measured in theequatorial plane, which is slightly less than the diameter, measuredunder the same conditions, which it has to have in the vulcanizationmold, and to be subjected to what is customarily called additionalshaping in the vulcanization mold. A crown reinforcement for a tire withradial carcass reinforcement, comprising one or more plies ofcontinuous, inextensible metal cables (that is to say those having anelongation of less than 0.2% under a tensile force equal to 10% of thebreaking load), makes said additional shaping under low tension possibleonly with great difficulty or not at all.

The use, as described for example in patent FR 2 013 812, ofinextensible metal cables which are discontinuous over a circumferentiallength has then proved judicious, firstly because it permits sufficientelasticity of the ply in the non-vulcanized state, and secondly becauseit permits the obtention in the vulcanized state of a modulus ofelasticity in tension of the ply which is very largely sufficient, saidmodulus being obtained by judicious selection of the length, whethervariable or not, of the cut cables and by the circumferential offset ofthe cuts.

The elasticity of the non-vulcanized ply is not only sufficient but toogreat for ready handling during production of the tire, and has provedto be the cause of laying irregularities, and in particularirregularities in the diameters of crown reinforcements for the varioustires of one and the same series.

It is obvious that the problem occurs in the same way with anyreinforcement which comprises metal cables, the lengths of which areless than the circumferential lengths of the parallel ones occupied inthe tire, insofar as it has been prepared independently of the buildingdrum and/or shaping drum for the non-vulcanized blanks of tire carcassreinforcements, without however inevitably having the same consequences.

SUMMARY OF THE INVENTION

With the aim of overcoming such production-related disadvantages, whilstnot adversely affecting the performance of the tire during travel, theinvention proposes a tire with carcass reinforcement, furthermorecomprising at least one additional reinforcement ply of maximumcircumferential length L, composed at least of lengths of metal wires orcables, of lengths of between 0.1 L and 0.5 L, arranged substantiallycircumferentially, parallel to each other and forming rows separatedfrom each other, in the direction perpendicular to their orientation, bygaps, characterized in that a textile cord or cable of syntheticmaterial is present in at least one gap out of two, and continuous overthe entire length of the rows.

"Length L of a reinforcement ply" for a tire is to be understood to meanthe maximum circumferential length of said ply.

The invention is particularly advantageous when the additionalreinforcement ply is a crown reinforcement ply of circumferentialcables, that is to say of cables forming an angle within the range ±2.5°with the circumferential direction of the tire.

"Cables arranged substantially circumferentially" are understood to meancables forming angles of between 0° and 15° with the circumferentialdirection of the tire.

Advantageously, the textile cord or cable is a cord or cable of lowdiameter, at most equal to 0.2 times the diameter of the metal cables ofthe ply, taking into account the fact that the breaking load of saidcord or cable will be at least equal to the tension to which the cord orcable has to be subjected in the non-vulcanized blank of the tire underthe action of the cambering pressure used for the shaping of said blank,and at most equal to 5 times said value, which permits the rupture ofsaid textile cords or cables of the ply during the vulcanization of thetire.

"Synthetic textile cord or cable" is to be understood to mean a cord orcable of rayon and/or of polyamide and/or of polyester and/or of anyother synthetic plastics material capable of being used for theproduction of textile fibers. Said textile cord or cable may be able tobe contracted under the action of heat, and will have as low as possiblea relative elongation under the action of the tension induced by theshaping pressure.

The production of a reinforcement ply with elements which arediscontinuous in the direction of the cords or cables may be effected invarious ways. One first way consists in producing a ply of continuouscords or cables according to one of the perfectly known methods, and tocut the cords or cables of the calendered ply thus formed into pieces atintervals, regular or not, spaced apart longitudinally. In order to cutthe reinforcement elements, manual cutting tools, or automatic cuttingtools, for example such as described in U.S. Pat. No. 3,844,327, may beused. This first method, which is already poorly suited to cutting cableby cable in the event that only metal cables are present, is absolutelyunsuited in the event that textile cords or cables, which are at greatrisk of being cut in risky manner as well, are present between the rowsof metal cables. A second method of producing the ply of discontinuouscables consists in laying, with slight pressure on a layer ofnon-vulcanized rubber mix which has previously been placed on acylindrical drum or on a table, sections of precut cord, or cables, saidlaying being effected in accordance with a layout arranged taking intoaccount the length of the lengths (which may be variable or constant),the distance between ends of the lengths in the longitudinal directionof the ply, the axial distance between lengths, which may also bevariable or non-variable, For the production of the ply according to thepresent invention, the continuous textile cord or cable which is unwoundfrom a supply reel, can be laid simultaneously. The lengths and the cordor cable having been laid, the ply is finished by depositing a secondlayer of non-vulcanized rubber mix on the lengths. In order to operatethis second method, the lengths of hooped cables may be used in the barestate and the textile cord or cable will be laid between the rows oflengths such that it is not in contact with said lengths, which requiresgreat laying accuracy and results in a lengthy and costly method. It isadvantageous to use lengths of coated cables, that is to say cablesaround which a cylindrical sleeve of rubber mix has already been laid byappropriate means, such as, for example, extrusion in which the rubbermix, emerging from a suitable die, is laid around the cord emergingthrough a guide orifice. Whilst it is preferable for hooped cables, theuse of coated cables is virtually compulsory for non-hooped cables.

Such a use, combined with the presence of an inserted textile cord orcable between two rows of lengths of metal cables, advantageouslypermits the production of a tire comprising a reinforcement ply withdiscontinuous circumferential cables, that is to say, cables which formangles within the range of ±5° with the direction of the tire. Themethod for producing such a ply consists in:

producing a strip composed of at least two contiguous rows of coated,discontinuous metal cables and, between each row, a sized continuoustextile cord or cable,

laying said strip on an inserted band of non-stick material, for examplepolyethylene, of a width substantially equal to twice the width of thestrip of cables, and winding the complex thus formed on a winding reel,

unwinding the strip in order to wind it in a coil around a cylindricaldrum or around a blank of carcass and/or crown reinforcements.

DESCRIPTION OF THE DRAWINGS

The characteristics and advantages of the invention will be betterunderstood with reference to the following description, which refers tothe drawing illustrating examples of embodiment in non-limitativefashion, in which:

FIGS. 1A and 1B show diagrammatically, a reinforcement ply according toa first variant of the invention, viewed respectively in plan view andin meridian section,

FIGS. 2A and 2B show, in the same manner, a reinforcement ply accordingto a second variant of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The reinforcement ply 1, which is intended to be a crown reinforcementply, the reinforcement elements 2, 3 of which will be orientedcircumferentially, is formed, firstly, of lengths 20 of hooped metal27.23 FR cables, said lengths 20 all being of the same length, and beingseparated circumferentially from each other by cuts 21. A row 2 oflengths 20 is axially separated from the axially adjacent row by a gapor pitch p, and in the case illustrated said pitch is axially constant(the pitch being the axial distance between the same two generatrices,respectively of two adjacent cables). These hooped cables are used inthe bare state and, after unwinding from one or more supply reel(s),pass over a conveyor, being guided by combs, to arrive in front of a setof cutting heads which, in accordance with a predetermined program, makethe cuts 21 as desired. Starting from one or more other reel(s), one ormore sized cord(s) 3 of aliphatic polyamide, that is to say cords coatedwith a composition based on rubber latex, resorcinol and formaldehyde,is (are) guided by suitable means so as to be arranged in all the gapsexisting between the rows of metallic lengths 20. The two series,respectively of metallic lengths 20 and of textile cords 3, areinserted, as is known, between two layers of non-vulcanized rubber mix,said two layers becoming the liner 4 of the ply 1 thus formed. As thetextile cords 3 have a diameter d of 0.25 mm in the case in question, itis preferable for the pitch p between two rows 2 of metallic lengths 20to be at least 1.9 mm, so as to avoid any possible contact between thesized textile cord 3 and the lengths 20 adjacent thereto.

FIG. 2 shows a reinforcement ply 1 formed from a strip 10 composed oftwo rows 2 of metallic lengths 20 of non-hooped 27.23 cables, coatedwith a sheath 5 of non-vulcanized rubber mix, said coated lengths 20being axially contiguous, and from a sized rayon textile cord, laidbetween and on the two rows of metallic lengths 20. The production ofsuch a strip comprises the following stages: two non-hooped metal cablesare coated with the non-vulcanized rubber sheath by known extrusionmeans, and are then cut to the desired lengths. The lengths 20 thusobtained are then guided by suitable means until they become contiguous,and the cord of sized rayon 3 is then deposited with slight verticalpressure on this assembly of two rows 2 of lengths 20. The strip 10,thus formed on a band of polyethylene, of a width equal to twice thediameter of a coated cable, is wound on a supply reel as a metal ortextile cable is usually wound, with a winding gap between the turns ofthe winding. The conventional known means can be used for the formationof the reinforcement ply 1: the strip 10 can be wound in a spiral arounda winding form, which may be a drum which is cylindrical or bulgesslightly transversely, on which a first layer of non-vulcanized rubberwill previously have been deposited; thus it is possible also to windthe strip 10 directly around the non-vulcanized blank of the carcassreinforcement of the tire to be manufactured, or the carcassreinforcement/crown plies assembly of said tire, as a function of thedesired radial positioning of the reinforcement ply 1 withcircumferential elements. A second layer of mix completes thereinforcement ply 1, and will form the liner 4 of the ply 1. It isobvious that the strip 10 can be produced from a number of rows 2 oflengths 20 greater than 2, without however reasonably exceeding thenumber of 5.

This principle of the formation of the reinforcement ply 1 offers theadvantage being able to use a rubber mix 5 which, after vulcanization,has properties of moduli, hysteresis loss, bonding etc. which aredifferent from those of the calendering mix 4: in the case described,the mix 5 is a mix which adheres strongly to the metal cables, with ahigh tangent modulus of tension under 10% relative elongation, whereasthe calendering mix 4 is a mix which adheres strongly to the size usedon the textile cords and with a tangent modulus of tension, measuredunder the same conditions, which is far less high. It is obvious thatthe strip 10 can be laid with a pitch P which is different from thetheoretical pitch p which exists between the two rows of lengths(theoretical because it is estimated between the generatrices of themetallic parts of the coated cables), and that various variantembodiments can be provided, as can numerous structural variants of thereinforcement ply 1.

I claim:
 1. A tire having carcass reinforcement, furthermore comprisingat least one additional reinforcement ply (1) of maximum circumferentiallength L, composed at least of lengths (20) of metal wires or cables, oflengths of between 0.1 L and 0.5 L, arranged substantiallycircumferentially, parallel to each other and forming rows separatedfrom each other, in the direction perpendicular to their orientation, bygaps (p, P), wherein a synthetic textile cord or cable (3) continuousover the entire length of the rows is present in at least one gap out oftwo.
 2. A tire according to claim 1, wherein the at least one additionalreinforcement ply (1) is a crown reinforcement ply and the lengths (20)of metal wires or cables arranged substantially circumferentially arelengths of circumferential metal cables.
 3. A tire according to claim 1,wherein the textile cord or cable (3) is a cord or cable of lowdiameter, at most equal to 0.2 times the diameter of the metal wires orcables of the at least one additional reinforcement ply (1).
 4. A tireaccording to claim 3, wherein the breaking load of the textile cord orcable (3) is a least equal to the tension to which the cord or cable isto be subjected in a non-valcanized blank of the tire under the actionof the cambering pressure to be used for shaping of said blank, and atmost equal to 5 times said tension.
 5. A tire according to claim 1,wherein the lengths (20) of metal wires or cables arranged substantiallycircumferentially are lengths of circumferential metal cables, thesynthetic textile cord or cable (3) is a sized rayon textile cord, andthe at least one additional reinforcement ply (1) is formed from a strip(10) composed of two axially contiguous rows of said lengths of metalcables coated with a sheath (5) of rubber mix, said rayon cord laidbetween and on said two rows of lengths of metal cables, and a liner (4)of rubber mix, said strip being spirally wound with a gap (P) greaterthan the gap (p) existing between said two rows of lengths of metalcables.